Find the formula to calculate the function shown on the screenshot

Good day It is necessary to create a module that will work with the Firebird database in C++ for selling products. There are examples of ready-made solutions and a description of the module's functionality. Main functions: authorization, selection of products on the screen from groups/subgroups, transition to the cart, payment by card, and printing the receipt. The program must work on Windows 10 and above, using the existing database.

Write and create a mobile application. A creative and highly professional approach is needed, as the idea of the application is not ordinary)

Development of a Power App, support for me as a beginner. Canvas App, assistance in developing the Screen Help in developing the data structure for the App Programming functions Assistance in creating Date-verse Tables